1. Field of the Invention
The present general inventive concept relates to radio frequency identification (RFID) communication, and more particularly, to a system to minimize interference between mobile RFID readers.
2. Description of the Related Art
An RFID system, one of systems employing radio-frequency identification technology, includes a tag (electronic tag or transponder) having peculiar identification information, and an RFID reader (reader or interrogator or radio frequency identification reader) capable of reading information of the tag using wireless communication. The RFID systems can be divided into mutual induction and electromagnetic wave types in accordance with a pattern of mutual communication between a tag and a reader, active and passive types in accordance with whether a tag is powered up by itself, or long-wave, medium-wave, short-wave, ultrashort-wave, and microwave types in accordance with frequency.
RFID systems using an ultrahigh frequency (UHF) band about 900 MHz are used in varieties of applications, accompanying with stationary and handheld readers, on basis of several standards such as ISO 18000-6 Type A/B EPC C1, C1-Gen2. In recent years, RFID systems are utilized for supply chain management (SCM), traceability management (TM), asset management (AM), and production management (PM).
Especially, the RFID system of UHF band makes it possible to conduct various application services because of long identification intervals. However, the RFID system inevitably connotes problems such as signal interference with variant wireless communication like cellular communication, or signal interference and conflict between readers in a multi-reader environment. To solve such problems, established is a spectrum mask in an RFID frequency band. And, a channel access scheme, such as frequency hopping (FP) or listening-before-talking (LBT), is proposed to solve the signal interference and conflict of the multi-reader environment, which cannot be resolved even by the spectrum mask.
In the meantime, a ubiquitous sensor network (USN) is a technique for identifying objects and environments by sticking electronic tags on all things, and establishing and utilizing real-time information by way of network. The USN is eventually directed to a communicable environment regardless of kinds of networks, devices, and services, anytime and anywhere, by granting computing and communicating functions to all things.
In efforts for achieving such a USN, an RFID reader function is included into a mobile phone. In this description, a mobile device, such a mobile phone including the RFID reader function, is referred to as mobile RFID reader. When the mobile RFID readers are used in a place, a single tag is accessed by a plurality of the mobile RFID readers.
For example, regarding a case of obtaining information about film screening, synopsis, and castings by accessing a tag attached to a movie poster by means of the RFID reader function, a plurality of users each having the mobile RFID readers are locating so near to each other (e.g., within several meters) and convenient to take points for accessing the tag. For that reason, the FP or LBT is not insufficient to resolve the signal interference and conflict between the mobile RFID readers.